Patients that need to use inhalers, such as pMDI devices, regularly have long had the need to be able to monitor their inhaler usage, and regulators of medicines have started to specify that some indication of when an inhaler is reaching the end of its recommended number of actuations as well as when it has reached or exceeded that number is integrated into the inhaler product. Dose counters (providing an accurate count of the number of doses remaining) and dose indicators (providing an indication of the number of doses remaining) have been proposed for use with inhalers. Yet, to date not many of the proposed dose counters or indicators for pMDIs have reached the market in a pMDI product. In most dose counters and dose indicators, the display is typically advanced each time the inhaler device is used, and it is particularly important that they do not undercount the number of dispensed doses as, in extreme cases, the patient may rely on the count shown on the pMDI device to receive life-saving medication. In dose counters or dose indicators, it may be acceptable for advancement of the display to be triggered (initiated) before or after the dose has been delivered, so long as it is practically impossible for the patient to trigger it without dispensing a dose. However, some of these dose counters or dose indicators are designed to require electronics which increases the cost, prevents the user from washing the device, may have battery life issues and, in the case of dose counters, may have difficulty obtaining regulatory approval for their use. In addition, many of these dose counters and/or dose indicators are complex requiring large numbers of small mechanical parts which gives rise to high costs, difficulties in assembly, and the requirement for complex dimensional tolerances. The added cost has long been a disincentive to product developers to incorporate a dose counter into an inhaler. In some instances, the dose counters and dose indicators require a re-design of what has become a standard shape and size of pMDI to significantly larger, bulkier and more awkward shapes. In addition, the character size and legibility of the display of such devices can be poor, making it difficult for a user to read them.
Examples of pMDI inhalers or devices having either dose counters or dose indicators are described in GB-A-1317315, WO-A-93/24167, U.S. Pat. No. 7,806,295, U.S. Pat. No. 5,421,482, U.S. Pat. No. 6,679,251, WO-A-02/91293, GB-A-2385640, WO-A-2006/119766, WO-A-2006/126965 and WO-A2008/025087.
GB-A-1317315 discloses a dose indicator that can be mounted in a pMDI actuator and which comprises four sets of advancement teeth which are sprung-loaded together. GB-A-2385640 discloses a dose indicator which is mountable within a pMDI actuator and which uses sets of fine teeth to advance the indicator.
WO-A-93/24167 discloses a two-component dose indicator that is mounted at the top of a pMDI actuator. WO-A-2006/126965 discloses a top-mounted dose indicator. WO-A-2008/025087 also discloses a top-mounted pMDI dose indicator in which an indicator ring component bears integral spring arms.
U.S. Pat. No. 7,806,295 discloses a dose indicator driven by a flexible tab attached to a ring. U.S. Pat. No. 5,421,482 discloses a mechanical dose indicator driven round by a ring of flexible arms on a rigid plate. WO-A-2006/119766 discloses a pMDI dose indicator comprising a single component for use with an unconventional rotary metering valve; thereby requiring modifications to the pMDI inhaler unit or to the actuator in which it is mounted.
U.S. Pat. No. 6,679,251 discloses a bottom-mounted pMDI dose counter which incorporates two C-springs the serve both to reset the dose counter and to provide follow-through for the valve firing of the inhaler. WO-A-02/91293 discloses a counter mechanism operated by a collapsible flexible ‘spider’.